In connection with the manufacture and/or recycling of polymeric materials, such as rubber, plastic, and the like, shredders and grinders have been used which employ rotating or whirling blades to cut, shred, and tear the polymeric material fed into a housing containing the blades. In the past, however, these devices have had substantial clearance between one blade and another and between the blades and the housing. Typically, the blades were thin, having a thickness less than about one-half of an inch (about 1.3 cm). Operation of such devices depended upon the thickness and momentum of the rubber or plastic material and the impact speed and the sharpness of the blades to cut, chip, and shred the polymeric materials into smaller piece sizes. Such devices have been inadequate for the purpose of shredding certain types of plastic for a number of reasons, especially in the case of thin-gauge plastic film. The throughput is limited. The plastic material rather than being cut or shredded, is often torn or merely stretched and pulled through the space between the blades. Plastic film often wraps itself around the rotating shafts in string fashion and clogs the throughput of the shredder. The tearing, stretching, and clogging also wears and dulls the blades and further reduces cutting or shredding efficiency. In the case of rotating parallel shafts having blades on them, the plastic material drawn between the shafts results in a high pressure wedging therebetween, which tends to cause the shafts to spread. The plastic thus passes through the machine without cutting. A sufficient buildup of woundup plastic sheet can result, causing friction within the machine, excessive heat buildup, and subsequent meltdown of the plastic material. Removal of the melted plastic requires complete shutdown and disassembly of the apparatus.
Some known plastic cutting machines which might be adapted for shredding plastic include a solid tub-shaped housing in which rotary blades operate. Maintenance and access to the interior of the housing requires that all of the blades be loosened from the shaft and that the shafts be withdrawn axially through an end of the housing. Thus, if meltdown occurs, if plastic clogging occurs, or if other foreign materials such as metals, wire, and the like are ingested into the machine, a time-consuming and costly and inefficient repair process must be implemented. In a continuous production line, shutdown of a single shredding machine can result in a shutdown of the entire production line, thereby multiplying the cost of the repairs significantly.